Matter Contrast Research Articles

Accelerated longitudinal gray/white matter contrast decline in aging in lightly myelinated cortical regions.

Highly myelinated cortical regions seem to develop early and are more robust to age-related decline. By use of different magnetic resonance imaging (MRI) measures such as contrast between T1- and T2-weighted MRI scans (T1w/T2w) it is now possible to assess correlates of myelin content in vivo. Further, previous studies indicate that gray/white matter contrast (GWC) become blurred as individuals' age, apparently reflecting age-related changes in myelin structure. Here we address whether longitudinal changes in GWC are dependent on initial myelin content within tissue as defined by baseline T1w/T2w contrast, and hypothesize that lightly myelinated regions undergo more decline longitudinally. A sample of 207 healthy adult participants (range: 20-84 years) was scanned twice (interscan interval: 3.6 years). Results showed widespread longitudinal reductions of GWC throughout the cortical surface, especially in the frontal cortices, mainly driven by intensity decay in the white matter. Annual rate of GWC blurring showed acceleration with age in temporal and medial prefrontal regions. Moreover, the anatomical distribution of increased rate of GWC decline with advancing age was strongly related to baseline levels of intracortical myelin. This study provides a first evidence of accelerated regional GWC blurring with advancing age, relates GWC patterns to cortical myeloarchitectonics and supports the hypothesis of increased age-related vulnerability of lightly myelinated areas. Hum Brain Mapp 37:3669-3684, 2016. © 2016 Wiley Periodicals, Inc.

Spatio-Temporal Patterns of Demyelination and Remyelination in the Cuprizone Mouse Model.

Cuprizone administration in mice provides a reproducible model of demyelination and spontaneous remyelination, and has been useful in understanding important aspects of human disease, including multiple sclerosis. In this study, we apply high spatial resolution quantitative MRI techniques to establish the spatio-temporal patterns of acute demyelination in C57BL/6 mice after 6 weeks of cuprizone administration, and subsequent remyelination after 6 weeks of post-cuprizone recovery. MRI measurements were complemented with Black Gold II stain for myelin and immunohistochemical stains for associated tissue changes. Gene expression was evaluated using the Allen Gene Expression Atlas. Twenty-five C57BL/6 male mice were split into control and cuprizone groups; MRI data were obtained at baseline, after 6 weeks of cuprizone, and 6 weeks post-cuprizone. High-resolution (100μm isotropic) whole-brain coverage magnetization transfer ratio (MTR) parametric maps demonstrated concurrent caudal-to-rostral and medial-to-lateral gradients of MTR decrease within corpus callosum (CC) that correlated well with demyelination assessed histologically. Our results show that demyelination was not limited to the midsagittal line of the corpus callosum, and also that opposing gradients of demyelination occur in the lateral and medial CC. T2-weighted MRI gray/white matter contrast was strong at baseline, weak after 6 weeks of cuprizone treatment, and returned to a limited extent after recovery. MTR decreases during demyelination were observed throughout the brain, most clearly in callosal white matter. Myelin damage and repair appear to be influenced by proximity to oligodendrocyte progenitor cell populations and exhibit an inverse correlation with myelin basic protein gene expression. These findings suggest that susceptibility to injury and ability to repair vary across the brain, and whole-brain analysis is necessary to accurately characterize this model. Whole-brain parametric mapping across time is essential for gaining a real understanding of disease processes in-vivo. MTR increases in healthy mice throughout adolescence and adulthood were observed, illustrating the need for appropriate age-matched controls. Elucidating the unique and site-specific demyelination in the cuprizone model may offer new insights into in mechanisms of both damage and repair in human demyelinating diseases.

B0 -orientation dependent magnetic susceptibility-induced white matter contrast in the human brainstem at 11.7T.

To investigate B0 -field-orientation dependent white matter contrast in the human brainstem based on R2 * and frequency difference (Δf) mapping from gradient echo (GRE) imaging at 11.7T. Multi-echo GRE data were acquired from two fixed human brainstem specimens at multiple orientations with respect to the static B0 field. The B0 -orientation dependent modulation curves of R2 * and Δf measurements between short and long echo time regimes were used to reconstruct maps of three-dimensional (3D) white matter orientation vectors. The results were compared with maps from diffusion MRI, susceptibility tensor imaging, and histological staining of the same specimens. R2 * and Δf maps demonstrated distinct and significant contrast modulation between the corticospinal tract (CST) and transverse pontine fibers (TPF) dependent on B0 orientation. Interleaved fiber orientations of the CST and TPF could be sensitively resolved based on field-orientation-dependent fitting of the R2 * and Δf measurements. The fitted 3D orientation vector maps and peak-to-peak amplitude of R2 * and Δf modulation exhibited close correspondence to primary eigenvector and anisotropy maps derived from diffusion MRI. The amplitude of B0 -orientation dependent R2 * modulation was significantly (P < 0.005) higher in the CST compared with TPF, while fractional anisotropies were comparable. The findings of this study demonstrate the potential of B0 -orientation dependent susceptibility-induced R2 * and Δf contrasts to probe tract-specific orientation and microstructure in white matter. Magn Reson Med 75:2455-2463, 2016. © 2016 Wiley Periodicals, Inc.

On-resonance variable delay multipulse scheme for imaging of fast-exchanging protons and semisolid macromolecules.

To develop an on-resonance variable delay multipulse (VDMP) scheme to image magnetization transfer contrast (MTC) and the chemical exchange saturation transfer (CEST) contrast of total fast-exchanging protons (TFP) with exchange rate above approximately 1 kHz. A train of high power binomial pulses was applied at the water resonance. The interpulse delay, called mixing time, was varied to observe its effect on the water signal reduction, allowing separation and quantification of MTC and CEST contributions as a result of their different proton transfer rates. The fast-exchanging protons in CEST and MTC are labeled together with the short T2 components in MTC and separated out using a variable mixing time. Phantom studies of selected metabolite solutions (glucose, glutamate, creatine, myo-inositol), bovine serum albumin (BSA), and hair conditioner show the capability of on-resonance VDMP to separate out exchangeable protons with exchange rates above 1 kHz. Quantitative MTC and TFP maps were acquired on healthy mouse brains using this method, showing strong gray/white matter contrast for the slowly transferring MTC protons, whereas the TFP map was more uniform across the brain but somewhat higher in gray matter. The new method provides a simple way of imaging fast-exchanging protons and MTC components with a slow transfer rate. Magn Reson Med 77:730-739, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Neurobiological origin of spurious brain morphological changes: A quantitative MRI study.

The high gray‐white matter contrast and spatial resolution provided by T1‐weighted magnetic resonance imaging (MRI) has made it a widely used imaging protocol for computational anatomy studies of the brain. While the image intensity in T1‐weighted images is predominantly driven by T1, other MRI parameters affect the image contrast, and hence brain morphological measures derived from the data. Because MRI parameters are correlates of different histological properties of brain tissue, this mixed contribution hampers the neurobiological interpretation of morphometry findings, an issue which remains largely ignored in the community. We acquired quantitative maps of the MRI parameters that determine signal intensities in T1‐weighted images (R 1 (=1/T1), R 2*, and PD) in a large cohort of healthy subjects (n = 120, aged 18–87 years). Synthetic T1‐weighted images were calculated from these quantitative maps and used to extract morphometry features—gray matter volume and cortical thickness. We observed significant variations in morphometry measures obtained from synthetic images derived from different subsets of MRI parameters. We also detected a modulation of these variations by age. Our findings highlight the impact of microstructural properties of brain tissue—myelination, iron, and water content—on automated measures of brain morphology and show that microstructural tissue changes might lead to the detection of spurious morphological changes in computational anatomy studies. They motivate a review of previous morphological results obtained from standard anatomical MRI images and highlight the value of quantitative MRI data for the inference of microscopic tissue changes in the healthy and diseased brain. Hum Brain Mapp 37:1801–1815, 2016. © 2016 The Authors. Human Brain Mapping Published by Wiley Periodicals, Inc.

New tissue priors for improved automated classification of subcortical brain structures on MRI

Despite the constant improvement of algorithms for automated brain tissue classification, the accurate delineation of subcortical structures using magnetic resonance images (MRI) data remains challenging. The main difficulties arise from the low gray-white matter contrast of iron rich areas in T1-weighted (T1w) MRI data and from the lack of adequate priors for basal ganglia and thalamus. The most recent attempts to obtain such priors were based on cohorts with limited size that included subjects in a narrow age range, failing to account for age-related gray-white matter contrast changes. Aiming to improve the anatomical plausibility of automated brain tissue classification from T1w data, we have created new tissue probability maps for subcortical gray matter regions. Supported by atlas-derived spatial information, raters manually labeled subcortical structures in a cohort of healthy subjects using magnetization transfer saturation and R2* MRI maps, which feature optimal gray-white matter contrast in these areas. After assessment of inter-rater variability, the new tissue priors were tested on T1w data within the framework of voxel-based morphometry. The automated detection of gray matter in subcortical areas with our new probability maps was more anatomically plausible compared to the one derived with currently available priors. We provide evidence that the improved delineation compensates age-related bias in the segmentation of iron rich subcortical regions. The new tissue priors, allowing robust detection of basal ganglia and thalamus, have the potential to enhance the sensitivity of voxel-based morphometry in both healthy and diseased brains.

Contrast-enhanced synthetic MRI for the detection of brain metastases.

BackgroundSynthetic magnetic resonance imaging (MRI), a technique that enables creation of various contrast-weighted images from a single MRI quantification scan, is a useful clinical tool. However, there are currently no reports examining the use of contrast-enhanced synthetic MRI for detecting brain metastases.PurposeTo assess whether contrast-enhanced synthetic MRI is suitable for detecting brain metastases.Material and MethodsTen patients with a combined total of 167 brain metastases who underwent quantitative MRI and conventional T1-weighted inversion recovery fast spin-echo (conventional T1IR) MRI before and after administration of a contrast agent were included in the study. Synthetic T1IR and T1-weighted (synthetic T1W) images were produced after parameter quantification. Lesion-to-white matter contrast and contrast-to-noise ratio were calculated for each image. The number of visible lesions in each image was determined by two neuroradiologists.ResultsThe mean lesion-to-white matter contrast and mean contrast-to-noise ratio of the synthetic T1IR images were significantly higher than those of the synthetic T1W (P < 0.001 and P < 0.001, respectively) and conventional T1IR (P = 0.04 and P = 0.002, respectively) images. Totals of 130 and 124 metastases were detected in the synthetic T1IR images by the first and second radiologists, respectively. The corresponding numbers were 91 and 85 in the synthetic T1W images and 119 and 119 in the conventional T1IR images. Statistical significance was not found among detected numbers of lesions.ConclusionSynthetic T1IR imaging created better contrast compared with synthetic T1W or conventional T1IR imaging. The ability to detect brain metastases was comparable among these imaging.

Comparison of 13N-NH3 and 18F-FDG PET/CT in the evaluation of gliomas

Objective To investigate the diagnostic efficacy of 13N-NH3 and 18F-FDG PET/CT in the evaluation of untreated gliomas. Methods A total of 45 consecutive patients (29 males, 16 females; age range 14-75 years, average age (47.47±15.64) years) with final diagnosis of glioma from August 2009 to May 2012 were retrospectively analyzed. PET/CT imaging was performed with both 18F-FDG and 13N-NH3. Imaging results were analyzed by tumor-to-gray matter (T/G) ratios. ROC curve analysis was conducted to determine the optimal T/G cutoff values between low-grade and high-grade gliomas. One-way analysis of variance was applied to assess the differential efficacy of the two tracers in different grade of glioma. Results Forty-eight separate lesions were identified (WHO grade Ⅱ, n=16; grade Ⅲ, n=12; and grade Ⅳ, n=20). The sensitivities of 13N-NH3 PET/CT and 18F-FDG PET/CT on predicting high-grade gliomas were 91%(29/32) and 66%(21/32), respectively. The optimal T/G cutoff values for 18F-FDG and 13N-NH3 were 0.64 and 0.86 with the AUC of 0.910 and 0.943, respectively. The sensitivity and positive predictive value of predicting high-grade gliomas with optimal cutoff values were 84% (27/32) and 93% (27/29) for 18F-FDG PET/CT, those for 13N-NH3 PET/CT were 94%(30/32) and 94%(30/32), respectively. Conclusion 13N-NH3 PET/CT is superior to 18F-FDG PET/CT not only in separating low-grade gliomas from high-grade ones, but also in the detection of high-grade gliomas for better tumor to normal gray matter contrast. Key words: Glioma; Tomography, emission-computed; Tomography, X-ray computed; Nitrogen radioisotopes; NH3; Deoxyglucose

Cerebral amyloid angiopathy-related inflammation: A potentially reversible cause of dementia with characteristic imaging findings

Cerebral amyloid angiopathy with inflammation (CAA-I) is a less well-recognized clinically and radiologically distinct subtype of CAA. We aim to describe the imaging manifestations of this uncommon entity. A retrospective review of the medical records and imaging database yielded 9 patients with clinical and radiological findings compatible with CAA-I. The neurological findings at presentation, MRI findings including the presence of white matter involvement, mass effect, microhemorrhages and contrast enhancement, treatment provided and outcome were evaluated. Brain biopsy specimens, when available were also reviewed. All patients presented with subacute cognitive decline. In all 9 patients, confluent white matter lesions with mass effect were observed. Eight out of 9 patients demonstrated foci of microhemorrhage, while in 1, the microhemorrhages appeared 12 weeks after the initial examination. No significant parenchymal or meningeal enhancement was present in any patient. In 4 patients, brain biopsy was consistent with CAA-I. Immunosuppressive therapy was initiated in all patients, leading to full recovery in 5. CAA-I is characterized by the subacute onset of dementia, a distinct pattern of confluent white matter signal abnormality with mass effect and response to immunosuppressive therapy. Prompt recognition may help obviate brain biopsy and initiation of treatment.

Optimization of image reconstruction conditions with phantoms for brain FDG and amyloid PET imaging.

The purpose of this study was to optimize image reconstruction conditions for brain (18)F-FDG, (11)C-PiB, (18)F-florbetapir and (18)F-flutemetamol PET imaging with Discovery-690 PET/CT for diagnosis and research on Alzheimer's disease (AD) based on the standard imaging protocols and phantom test procedures and criteria published by the Japanese society of nuclear medicine (JSNM). A Hoffman 3D brain phantom and a cylindrical pool phantom were scanned according to the JSNM procedure, and the reconstruction conditions (iteration, subset, post-filter) were optimized so that the images satisfy the JSNM criteria regarding spatial resolution (FWHM ≤ 8 mm) and gray/white matter contrast (%contrast ≥ 55%) on the Hoffman phantom and uniformity (SD of small ROIs ≤ 0.0249) and image noise (coefficient of variation ≤ 15 %) on the pool phantom. Human images were acquired with (18)F-FDG (15-min scan starting at 30 min post-injection [p.i.] of 185 MBq), (11)C-PiB (20-min scan starting at 50 min p.i. of 555 MBq), (18)F-florbetapir (10-min scan starting at 50 min p.i. of 370 MBq) and (18)F-flutemetamol (30-min scan starting at 90 min p.i. of 185 MBq) on 1 or 2 subjects for each tracer and reconstructed with thus determined conditions to evaluate the image quality visually. The effect of reconstruction parameters on the standardized uptake value ratio (SUVR) was also evaluated on 5 amyloid-positive and 5 amyloid-negative PiB images. A sufficient image quality was obtained at an iterative update (product of iteration and subset) of 64 for (18)F-FDG. The same reconstruction parameters with an additional Gaussian filter of 5 mm FWHM was optimal for (11)C-PiB, (18)F-florbetapir and (18)F-flutemetamol to achieve the phantom criteria. Those optimal reconstruction conditions were confirmed with human images. The SUVR value was stable over a wide range of iterative updates around the optimal parameters both for positive and negative amyloid images. Optimal image reconstruction conditions were determined for brain (18)F-FDG and amyloid PET imaging with Discovery-690 PET/CT for diagnosis and research on AD based on the JSNM phantom criteria. This supports feasibility of the phantom criteria for standardization and harmonization of brain (18)F-FDG and amyloid PET for multicenter studies.

Time-efficient, high-resolution, whole brain three-dimensional macromolecular proton fraction mapping.

Macromolecular proton fraction (MPF) mapping is a quantitative MRI method that reconstructs parametric maps of a relative amount of macromolecular protons causing the magnetization transfer (MT) effect and provides a biomarker of myelination in neural tissues. This study aimed to develop a high-resolution whole brain MPF mapping technique using a minimal number of source images for scan time reduction. The described technique was based on replacement of an actually acquired reference image without MT saturation by a synthetic one reconstructed from R1 and proton density maps, thus requiring only three source images. This approach enabled whole brain three-dimensional MPF mapping with isotropic 1.25 × 1.25 × 1.25 mm(3) voxel size and a scan time of 20 min. The synthetic reference method was validated against standard MPF mapping with acquired reference images based on data from eight healthy subjects. Mean MPF values in segmented white and gray matter appeared in close agreement with no significant bias and small within-subject coefficients of variation (<2%). High-resolution MPF maps demonstrated sharp white-gray matter contrast and clear visualization of anatomical details, including gray matter structures with high iron content. The proposed synthetic reference method improves resolution of MPF mapping and combines accurate MPF measurements with unique neuroanatomical contrast features.

3T-MRI in patients with pharmacoresistant epilepsy and a vagus nerve stimulator: A pilot study

For safe 3T-MRI of patients with VNS (vagus nerve stimulator), specific conditions are mandatory. However, application of these conditions can lead to a loss of image quality. In this work, we evaluated the diagnostic value of 3T-MRI in VNS patients with pharmacoresistant epilepsy. Using a transmit-and-receive head coil and adapting our sequences to allow for low SAR (specific absorption rate), we examined 15 patients with pharmacoresistant epilepsy. Diagnostic quality was assessed by comparison of the SNR (signal to noise ratio) and CNR (contrast to noise ratio) of the hippocampus, the grey-white matter contrast and epileptogenic lesions to images of patients without VNS acquired with our routine 3T-MRI protocol and the 32-channel head coil. 3T-MRI is feasible in VNS-patients. Image quality is adequate for detection and follow-up of epileptogenic lesions such as ganglioglioma or PNH (periventricular nodular heterotopia). Due to a significant reduction of SNR and CNR, the diagnostic value for subtle lesions may be decreased. Overall, the feasibility of 3T-MRI is beneficial in the diagnostic workup and follow-up of epilepsy-patients with VNS.

Investigation of (11)C-PiB equivocal PET findings.

We have encountered occasional equivocal findings when assessing cerebral cortical amyloid retention with (11)C-Pittsburgh compound B (PiB) PET. We investigated the diagnostic significance of equivocal PiB PET findings. This retrospective study included 101 consecutive patients complaining of cognitive disorders (30 Alzheimer's disease, 25 mild cognitive impairment, 8 Lewy body disease, 7 frontotemporal lobar degeneration, 31 others) who underwent both (11)C-PiB PET and (18)F-fluorodeoxy-D-glucose (FDG) PET. We visually classified PiB-positive, PiB-equivocal or PiB-negative ratings according to cortical uptake. For quantitative assessments of PiB PET, standard uptake values referred to cerebellar cortex (SUVR) were calculated in regional template volume of interests (frontal, temporoparietal, precuneus/posterior cingulate cortex, cerebral white matter and cerebellar cortex). The results of visual assessment were compared with the regional and mean cortical SUVRs and cortical-to-white matter ratio of PiB uptake, as well as clinical and FDG PET findings. Among the 101 scans, 41 were PiB negative, 11 were PiB equivocal, and 49 were rated PiB positive in the visual assessments. The mean cortical SUVR and cortical-to-white matter ratio were 0.97 ± 0.07 and 0.57 ± 0.21 in PiB-negative, 1.51 ± 0.17 and 0.75 ± 0.06 in PiB equivocal and 2.10 ± 0.33 and 0.97 ± 0.11 in PiB-positive group, respectively. Nine of 11 subjects with PiB-equivocal findings had cognitive impairments and FDG distribution compatible with Alzheimer's disease or dementia with Lewy bodies. We considered equivocal visual findings on PiB PET equivalent to PiB-positive with slight cortical uptake. In addition, slight cortical amyloid deposits were considered to cause cerebral metabolic abnormality and cognitive impairment. Although mean cortical SUVR was more sensitive than visual assessment because of low cortical-to-white matter contrast due to non-specific accumulation in white matter, it is important not to overlook small amounts of cortical uptake of PiB in visual inspection for exact diagnosis.

An automated tool for cortical feature analysis: Application to differences on 7 Tesla T2* -weighted images between young and older healthy subjects.

High field T2* -weighted MR images of the cerebral cortex are increasingly used to study tissue susceptibility changes related to aging or pathologies. This paper presents a novel automated method for the computation of quantitative cortical measures and group-wise comparison using 7 Tesla T2* -weighted magnitude and phase images. The cerebral cortex was segmented using a combination of T2* -weighted magnitude and phase information and subsequently was parcellated based on an anatomical atlas. Local gray matter (GM)/white matter (WM) contrast and cortical profiles, which depict the magnitude or phase variation across the cortex, were computed from the magnitude and phase images in each parcellated region and further used for group-wise comparison. Differences in local GM/WM contrast were assessed using linear regression analysis. Regional cortical profiles were compared both globally and locally using permutation testing. The method was applied to compare a group of 10 young volunteers with a group of 15 older subjects. Using local GM/WM contrast, significant differences were revealed in at least 13 of 17 studied regions. Highly significant differences between cortical profiles were shown in all regions. The proposed method can be a useful tool for studying cortical changes in normal aging and potentially in neurodegenerative diseases. Magn Reson Med 74:240-248, 2015. © 2014 Wiley Periodicals, Inc.

GPU-accelerated Monte Carlo based scatter correction in brain PET/MR.

To develop and evaluate a fast and accurate Monte Carlo simulation (MCS) based scatter correction for PET/MR imaging, based on Geant4 using graphical processing units (GPUs). The GPU implementation by Bert et al. [1] including the photon tracking within a voxelized volume was extended with the modeling of the detection process in the Siemens MR-BrainPET. Using NVIDIA’s CUDA photon pairs undergo several kernel functions in parallel, from their generation according to the activity distribution up to their detection in the scanner. Subsequently, coincidences are sorted and stored in list-mode. The new GPU implementation (GeForce GTX690) was validated by comparison with Gate v6.2 on a single CPU (Intel Core i7, 3.4GHz), showing a speedup factor of 135. The use of multiple GPUs can further increase this acceleration. For Compton scatter correction the reconstructed emission image, the patient MR-derived attenuation map and a CT-derived attenuation template of the MR coils are used as input for the simulation. The resulting simulated projection data are scaled to the normalized measured projection data. Thus, the often unstable fit to the distribution tails, necessary for single scatter simulation (SSS)[2], is circumvented. The scaled simulated scatter distribution is then incorporated in the reconstruction. The proposed scatter correction methodology was evaluated and compared to the SSS approach using sphere phantom measurements. Finally, the effect on patient data was investigated. Phantom results suggest an improved contrast with our new MC-based scatter correction, especially for measurements including the MR coils, where the contrast recovery was improved by 10-14%. First patient images also show improved grey/white matter contrast. Table 1 Comparison of recovery coefficients after scatter correction based on MCS and SSS. MC-based scatter correction shows improved recovery coefficients for the hot spheres. Figure 1 Assessment of image quality according to NEMA NU 2-2007. Images show the phantom with a hot spheres/background ratio of 8:1 measured with MR head coils inside the BrainPET scanner. Figure 2 Comparison of reconstructed FDG images using the scatter estimate provided by the vendor’s SSS (left) and our MCS method (right). Images were reconstructed using the vendor provided 3D OP-OSEM algorithm with 2 subsets and 32 iterations. The new GPU-accelerated MCS allows for fast and accurate estimation of scattered coincidences in PET studies using the Siemens MR-BrainPET with a major speed-up compared to standard MCS and superior image quality compared with the standard correction based on SSS.

VALIDATION OF HIPPOCAMPAL TEXTURE FOR EARLY ALZHEIMER'S DISEASE DETECTION: GENERALIZATION TO INDEPENDENT COHORTS AND EXTRAPOLATION TO VERY EARLY SIGNS OF DEMENTIA

neurofibrillary tangles than LOAD patients. However, these findings have not been substantiated in clinical studies. Studies using Positron Emission Tomography (PET) with carbon-11-labelled Pittsburgh compound-B (PiB) were not conclusive in replicating the post-mortem findings. A previous study suggested that iron accumulation, which may reveal AD pathology and more specifically amyloid deposition, is reflected by phase information from 7T T 2*-weighted MRI sequences. The aim of this study is to explore regional iron-related differences in the cerebral cortex, indicative of AD pathology, between EOAD and LOAD patients using 7T MR phase images. Methods: 12 EOAD patients, 17 LOAD patients and 17 healthy elderly controls (table 1) were scanned at 7T using a 2D transverse T 2*-weighted scan with a total imaging duration of 10 minutes. MRI scans were analyzed quantitatively by measuring lobar peak-to-peak phase shifts in the frontal, parietal, and left and right temporoparietal regions. Cortical parcellation was performed on the T 2*-weighted images using the segmented cortex and an anatomical atlas (AAL atlas) (figure 1). The regional mean gray matter (GM)/ white matter (WM) contrast was computed as the difference between the mean phase value of the GM and WM ROIs. Results: An increased peak-to-peak phase shift was found for all lobar regions in EOAD patients compared with LOAD patients (p1⁄40.05) (table 2). Regional mean phase contrast in EOAD patients was higher than in LOAD patients in the superior medial and middle frontal gyrus, anterior and middle cingulate gyrus, postcentral gyrus, superior and inferior parietal gyrus, and precuneus (p<0.042) (table 3). Conclusions: These data suggest that EOAD patients have an increased iron accumulation, as compared with LOAD patients, in specific cortical regions, which could also be related to increased amyloid deposition.

A study-specific fMRI normalization approach that operates directly on high resolution functional EPI data at 7 Tesla

Due to the availability of ultra-high field scanners and novel imaging methods, high resolution, whole brain functional MR imaging (fMRI) has become increasingly feasible. However, it is common to use extensive spatial smoothing to account for inter-subject anatomical variation when pooling over subjects. This reduces the spatial details of group level functional activation considerably, even when the original data was acquired with high resolution. In our study we used an accelerated 3D EPI sequence at 7Tesla to acquire whole brain fMRI data with an isotropic spatial resolution of 1.1mm which shows clear gray/white matter contrast due to the stronger T1 weighting of 3D EPI. To benefit from the high spatial resolution on the group level, we develop a study specific, high resolution anatomical template which is facilitated by the good anatomical contrast that is present in the average functional EPI images. Different template generations with increasing accuracy were created by using a hierarchical linear and stepwise non-linear registration approach. As the template is based on the functional data themselves no additional co-registration step with the usual T1-weighted anatomical data is necessary which eliminates a potential source of misalignment. To test the improvement of functional localization and spatial details we performed a group level analysis of a finger tapping experiment in eight subjects. The most accurate template shows better spatial localization – such as a separation of somatosensory and motor areas and of single digit activation – compared to the simple linear registration. The number of activated voxels is increased by a factor of 1.2, 2.5, and 3.1 for somatosensory, supplementary motor area, and dentate nucleus, respectively, for the functional contrast between left versus right hand. Similarly, the number of activated voxels is increased 1.4- and 2.4-fold for right little versus right index finger and left little versus left index finger, respectively. The Euclidian distance between the activation (center of gravity) of the respective fingers was found to be 13.90mm using the most accurate template.

White and gray matter contrast enhancement in MR images of the mouse brain in vivo using IR UTE with a cryo-coil at 9.4 T.

The aim of this work was to assess the capability of high field MRI to image brain micro-structures containing various amount of myelin. A cryogenic RF receiver coil (Bruker 'CryoProbe') and an ultra-short echo (UTE) 2D pulse sequence with and without inversion pulse were used for coronal brain MR imaging of a healthy C57BL/6J mouse. A 9.4 T magnet system was used. Signal-to-noise ratio (SNR) within the selected regions was measured. A room temperature volume RF coil was also used for SNR comparison. The inversion recovery IR-UTE 2D pulse sequence was optimized for maximum white matter (WM) and gray matter (GM) contrast-to-noise ratio (CNR). The results showed 3- to 12-fold improvement in SNR for the cryo-coil compared to the volume coil depending on the area. The inversion times providing optimum CNR for WM and GM were found to be 500 ms (negative CNR) and 1000 ms (positive CNR) for the echo time of 350 μs. Presented method provide better SNR and CNR for the brain structures with short T2 than the current techniques. The results indicate that the optimized IR-UTE pulse sequence when used with the cryo-coil allows for over 10-fold enhancement of the CNR for WM and GM as compared to the standard UTE without inversion pulse.

Significance of enhanced cerebral gray–white matter contrast at 80 kVp compared to conventional 120 kVp CT scan in the evaluation of acute stroke

We aimed to determine whether 80kVp conventional nonenhanced head CT scans have better gray–white matter contrast than standard 120kVp scans performed on the same patients. Thirty head CT scans acquired at 80kVp (CT dose index [CTDI]vol 46) were compared to prior studies in the same patients performed at 120kVp (CTDIvol 59). Signal (Hounsfield units [HU]), noise (sd HU), and contrast-to-noise ratio per dose (CNRD) were assessed in multiple cerebral gray and white matter regions of interest. A noise correction factor was used to compensate for scanning at different CTDIvol values. Average gray matter signal at 80kVp and 120kVP was 33.9±3.5HU and 29±4.6HU, respectively (p<0.0001); the averages for white matter were 22.5±3.1HU and 21.6±4.6HU, respectively (p=0.11). Corrected noise was 3±0.6 and 2.7±0.6, respectively, for gray matter (p=0.0001), and 2.8±0.6 and 2.6±0.5, respectively, for white matter (p=0.00001). The gray–white matter CNRD was 4.0±1.2 at 80kVp and 2.8±1 at 120kVp (p<0.00001). Cerebral gray–white matter CNRD is increased by 40% at 80kVp compared to conventional 120kVp CT scans. These findings justify further clinical evaluation in the acute stroke setting.

Technical review, types of imaging, part 4--magnetic resonance imaging.

Technical review, types of imaging, part 4--magnetic resonance imaging.